In a production process of a semiconductor element, an original pattern in which a circuit pattern is formed, that is, a mask or a reticle (hereinafter collectively referred to as a mask) is exposed and transferred onto a wafer by a reduction projection exposure apparatus called a stepper or a scanner. Since production of a Large Scale Integration (LSI) requires a large manufacturing cost, it is crucial to improve the production yield, however, a defect of a mask pattern can be cited as a large factor of degradation in the production yield of a semiconductor element. Accordingly, it is important to detect a defect in an inspection process during a mask production process.
Further, it is also important to measure a line width (CD) of a pattern formed in a mask; generate a map of a distribution of a difference value (line width error: ΔCD) between the measured value of the line width and the design value of the pattern; and feed back the map to the mask production process. According to a conventional method, a line width for each pixel is measured based on an optical image of a pattern and a reference image generated from design data of the pattern. For example, in a case where the pattern is a line pattern, one edge to be a starting point for a measurement of a line width of the pattern, and another edge corresponding to that edge, to be an ending point for the measurement of the line width of the pattern, are respectively detected with an accuracy of one pixel or less. Then, the line width is obtained by measuring a distance between these edges (see Japanese Laid-Open Patent Publication No. 2003-214820).
With high integration and large capacity of a Large Scale Integration (LSI), a circuit dimension required for a semiconductor element has become increasingly narrowed. That is, a pattern of the LSI to be formed on a semiconductor wafer has become finer, and a pattern to be formed on a mask has also become finer. When the pattern becomes finer, it is difficult to accurately obtain a line width of the pattern, and as a result, a value of a line width error may become larger than an actual value of the line width error. Further, an optical image of the mask is acquired by irradiating the mask with light from a light source, wherein the light is transmitted through the mask or reflected by the mask, into a sensor. In this case, when a light quantity of the light source fluctuates, the value of the line width error will be different to the actual value of the line width error.
The present invention has been made in view of the above-mentioned problems. That is, an object of the present invention is to provide a line width error of a pattern formed in a sample obtaining method that can accurately obtain a line width error.
Further, another object of the present invention is to provide a line width error of a pattern formed in a sample obtaining apparatus that can accurately obtain a line width error.
Further, another object of the present invention is to provide an inspection system including a function that can accurately obtain a line width error.
Other challenges and advantages of the present invention are apparent from the following description.